1. Field of the Invention
The invention relates to a method for operating a power plant. The invention also relates to a power plant for carrying out this method.
2. Brief Description of the Related Art
Throughout the world, a significant proportion of power generation is based on combustion reactions in which fossil fuels are burnt. As far as it is possible to predict, this will also continue to be the case in the future. However, firstly the combustion of fossil fuels is irrevocably linked to the production of carbon dioxide. Secondly, the increase in the carbon dioxide concentration in the atmosphere is regarded as being a primary cause of global warming. To allow environmentally friendly use of fossil fuels, there are numerous known measures which can be used to reduce the emissions of pollutants and greenhouse gases. By way of example, greenhouse gas emissions can be reduced by operating power plants more economically through increasing their efficiencies. Furthermore, the use of fuels which have a relatively high hydrogen/carbon ratio leads to reduced emission of greenhouse gases. However, fuels of a high hydrogen/carbon ratio, such as for example crude oil and natural gas, are unavailable or have only restricted availability in some parts of the world, which is attributable to geographic and/or political consideration. By way of example, the USA and China each have extensive coal reserves, making this fuel correspondingly inexpensive. Accordingly, in these regions the generation of power based on the combustion of coal will continue to be of relatively great importance, and consequently measures are required to lower the carbon dioxide emissions in this field.
WO 2004/042200 A1 has disclosed a power plant which includes a compressor, a turbine and a burner arrangement with a pre-burner and an afterburner. There is also an oxygen-removal device, which can remove some of the oxygen contained in the combustion exhaust gases from the pre-burner therefrom. The oxygen removed from the combustion exhaust gas from the pre-burner can be discharged from the oxygen-removal device by means of a sweep gas with the aid of a sweep gas device. Dividing the burner arrangement into a pre-burner and an afterburner, combined with the removal of some of the oxygen gas contained in the combustion exhaust gas from the pre-burner from this exhaust gas, means that in this combustion process, in addition to hot combustion exhaust gases which can be expanded in the turbine, gaseous oxygen is thus additionally produced and can then be utilized in basically any desired way. Arranging the oxygen-removal device between the two burners ensures that the oxygen-removal device can operate at relatively high but not excessively high temperatures, which are provided by means of the combustion exhaust gases from the pre-burner. Then, in the subsequent after burning, the temperature is increased further, in order to enable a combustion exhaust gas with a particularly high energy content to be fed to the turbine.
In the known power plant, the sweep gas used is a mixture of natural gas and steam. In the known power plant, the oxygen-removal device simultaneously serves as a partial oxidation reactor which converts the natural gas supplied at least into hydrogen and carbon monoxide.
In the known power plant, therefore, the oxygen-removal device is exposed to relatively high thermal stresses, which shorten the service life of the oxygen-removal device.